It's a custom profile field. You can easily delete it without much pain. Not sure it would be present on a fresh install but you're welcome to check and report it. We wouldn't delete it on an upgrade however.

Umm no, 25% does not equal most. 51% equals most. Twitter is heavily used in Russia and Arab countries, especially for political protests.

Windows Live Messenger is not discontinued in China yet, but it will be soon. But even if it wasn't, if you are going to cater to China, then you should be including Baidu and tons of other Chinese messengers, which are much bigger than WLM, and if you're going to cater to other specific Asian countries, you should include KaKaoTalk, Line, etc.